The role of surface chemistry and solution pH on the removal of Pb2+ and Cd2+ ions via effective adsorbents from low-cost biomass

A deep understanding of adsorption of Pb2+ and Cd2+ ions from their aqueous solutions on activated carbons and their HNO3-oxidized forms has been attempted. These activated carbons were obtained from date pits using different activation methods. Adsorption isotherms of Pb2+ and Cd2+ ions were determined from solutions at pH 3 and 5.9. The results revealed that all obtained isotherms exhibited the model fitting according to Langmuir equation. The oxidized samples prone, slightly, to the high affinity isotherm type. The results revealed also that the investigated carbons removed appreciable amounts of lead and cadmium ions which increased by increasing pH of solutions from 3 to 5.9. The adsorption capacity of the investigated carbons also increased by HNO3 acid surface treatment. The results were discussed in light of a possible chemical modification by nitric acid resulting in the creation of a large number of surface functional oxygen species. This interpretation was confirmed by FrlR investigation. The solution-pH and the surface chemistry of the carbons were found to play a decisive role in the uptake of these heavy metal ions from aqueous solutions rather than the carbon texture characteristics. (C) 2008 Elsevier B.V. All rights reserved.